The big spring divide

While many plants prefer to be divided in autumn and settled into the still-warm soil for their winter sojourn, there are several exceptions. Late-flowering perennials, for example, which fill our beds and borders with colour come September and October, won't thank you for splitting them into pieces when they have just had the good grace to give their all. It takes a lot of energy to produce flowers, and while the astrantias and campanulas of high summer have had a chance to recuperate, these late performers will be pretty knackered, so it's much more considerate to wait until spring before dividing them.

Likewise, any and all of the Michaelmas daisy tribe should be divided in spring. You can also tackle anything that grows in a similar way - that is, anything with a loose crown that roots as it spreads outwards. This includes the multitude of big, yellow prairie daisies, rudbeckia, perennial sunflowers and chrysanthemums.

While the bully brigade may storm in with a sharp spade and strong biceps, chopping up everything in sight, a gentler approach yields a greater bounty. These clumps are seldom deep-rooted, and a garden fork is therefore by far the most effective tool for lifting them. Shake the soil from the roots, or if, like me, you garden on heavy clay, swish them around in a bucket of water so you can see what you are dealing with. Work your fingers and thumbs into the centre of the clump, pulling off small-rooted pieces. When you get to the unproductive heart, it's beyond resuscitation, so just discard it.

These rooted sections used to be known as "Irishman's cuttings" (though perhaps these days we should more correctly call them "Irish person's cuttings"). Plant them into fresh soil mixed with a good few handfuls of homemade compost or any well-rotted organic material. Space them a few inches apart, so they put on a good show, or pot several to a roomy container.

This year we are going to experiment by giving each small-rooted piece a place of its own in a cell tray. When all are happily established by late April, we will plant them out in big groups to give a knockout show next autumn.